Electronic devices that are portable, such as radiotelephones, permit a user to communicate telephonically over a wireless system from virtually any location. To facilitate portability, it is known to make a radiotelephone closeable so that it has an opened position and a closed position. In the opened position, a user interface of the radiotelephone, which includes a speaker, a microphone, a display, and a keypad, is fully exposed and the radiotelephone has a length that is sufficient to allow the ear and mouth of the user to align with the speaker and microphone, respectively, to enable telephonic communication. In the closed position, the user interface is overlapped or collapsed thereby making the radiotelephone shorter in length and easily transportable.
One type of closeable radiotelephone employs two housings joined by a hinge that allows the housings to fold upon one another in the closed position. One such hinge is hinge 301 of radiotelephone 100 shown and described in U.S. Pat. No. 5,628,089 by Wilcox et al., entitled "Radiotelephone Having A Self Contained Hinge," issued May 13, 1997, and assigned to Motorola, Inc. The hinge 301 comprises a follower 403, a cam 404, and a spring 405 assembled into a cylindrically hollow can 303 via an open end thereof and held in assemblage by a cap 305 coupled to the can 303 over the open end. The cam 404 includes rails 417 that slidably engage corresponding guides 437 formed in, and running the length of, the interior surface 465 of the can 303. The can 303 is fabricated from a plastic injection molding process that releases the can 303 from the mold in the same direction as its center axis. In order to eject the can 303 from such a molding process, a draft angle in the interior surface 465 is employed. The draft angle causes the interior surface 465 and the width of the guides 437 to taper opposite the open end and, thus, cause variation in the diameter along the interior surface 465 and in the width of the guides 437. When the radiotelephone 100 is moved between the closed and opened positions, cam 404, aside from translating along the center axis of the can 303, displaces or rotates due to the nonuniformity of the interior surface 465 and the guides 437. This causes the rails 417 to hit the edges of the guides 437 and produce an audible clicking noise. The clicking noise, while desirable to those users who wish to receive audible feedback that the radiotelephone 100 is entering the closed or open position, may be undesirable to other users.
Thus, a need exists for a hinge suitable for use in a foldable device, such as a portable radiotelephone, that minimizes noise when the foldable device is moved between the closed and opened positions.